1. Field of the Invention
The present invention relates generally to a method and apparatus for fabricating semiconductor devices and, in particular, to a method and apparatus for cleaning a substrate surface by, for example, eliminating polysilicon defects induced by metallic contaminants.
2. Description of Related Art
In the production of semiconductor devices, a semiconductor substrate, such as a silicon substrate, may be formed comprising a number of varying block levels or layers whereby such block levels may include various structures formed over the semiconductor substrate. For example, block levels may include varying structures over the silicon substrate which define the semiconductor devices such as resistors, PFET wells and NFET wells in CMOS technology, and the like.
As will be recognized, the varying structures, or varying block levels, may be made by processes including photolithography, ion implant, resist strip, wet cleaning processes, and the like. An inherent problem of these block levels, and the processes used to define them over the silicon substrate, is that they produce contaminants including, for example, metallic contaminants and hydrocarbon-containing contaminants over the substrate which remain thereon to contaminate the surface. During the semiconductor manufacturing process, contaminants including metallic contaminants and hydrocarbon-containing contaminants may be deposited on both the substrate front-side (chip side) and back-side. Front-side contaminants are typically introduced from trace metallics in the photoresist while backside contaminants are typically introduced from the semiconductor processing equipment such as, for example, automated substrate handlers and chucks. This invention addresses both substrate front-side and back-side metallic removal.
As will be further recognized, if the metallic contaminants are not removed from the substrate front-side or back-side prior to either the gate oxidation or the polysilicon deposition processes, a gross defect may be induced. It is preferable to remove the contaminants prior to gate oxidation to reduce the potential for gate oxide xe2x80x9cpinholesxe2x80x9d. These xe2x80x9cpinholesxe2x80x9d can render the device either non-functional or unreliable due to poor gate oxide integrity. Additionally, removal of the metallic contaminants will prevent the formation of polysilicon defects, herein referred to as xe2x80x9cpeppery polysiliconxe2x80x9d, which can result in shorts between polysilicon lines.
The microelectronics industry has faced problems with peppery polysilicon since it first started using polysilicon as a gate conductor. Several techniques are aimed at controlling peppery polysilicon including, for example, reducing the metallics within the deposited photoresist, and improving both the dry steps and wet clean steps used to define the various block levels. However, such prior art techniques do not completely eliminate the metallic contaminants over the substrate surface, and thus do not prevent the occurrence of peppery polysilicon. Therefore, known techniques can still lead to semiconductor failure in the field.
Prior art is also directed to controlling contaminants within the deposition tools used for gate formation. For instance, in U.S. Pat. No. 3,279,946, a process is disclosed wherein a reactor chamber, or a conventional semiconductor deposition tool, is preconditioned prior to a semiconductor material deposition. The tool is preconditioned by heating the reactor in the presence of a reactant gas, preferably HCl or chlorine, which reacts with donor impurities on the walls of the chamber to merely remove impurities in the reactor prior to a semiconductor material deposition on a clean wafer. This approach is problematic as the chlorine eventually induces corrosion of the deposition tooling in the reactor whereby the corrosion can actually increase metallic contamination during the semiconductor material deposition. Since the prior art does not describe any in-situ cleaning of metal contaminants from a substrate surface, or cleaning of the corroded deposition tooling, peppery polysilicon will likely result and the semiconductor may fail.
Furthermore, as semiconductor technologies, such as CMOS technologies, continue to decrease in size, and thus require thinner transfer gate oxides, the known cleaning and/or metallic contamination removal processes do not completely clean the substrate surface and/or eliminate metallic contaminants from the substrate surface. For example, the process of removing metallic contaminants from a substrate surface using a chlorinated environment during gate oxidation transfer processes is used for thick gate oxide depositions. In such processes, the metallics are removed as a result of the substrate being exposed to the chlorinated environment for the extended period of time it takes to deposit the thick gate oxide. However, such techniques are not effective or efficient in removing metallic contaminants from substrates having thin gate oxide. To produce the thinner gate oxide the substrate will be exposed to the chlorinated environment for a limited time since the gate oxide deposition time is reduced to produce the thinner gate oxide. Thus, metallic contaminants may remain on the thin gate oxide resulting in peppery polysilicon, as well as pinholes in the thinner gate oxide, whereby gate oxide integrity may be compromised, and polysilicon shorts and semiconductor failure may occur.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method and apparatus which cleans and/or removes contaminants, including metallic contaminants and hydrocarbon-containing contaminants, form a surface of a substrate to provide the substrate with a clean surface for uniform gate formation.
It is another object of the present invention to provide a method and apparatus to clean and/or reduce residual metallic contamination on a surface of a semiconductor substrate after completion of all block levels.
A further object of the present invention is to provide a method and apparatus to clean and/or reduce residual metallic contamination on a surface of a semiconductor substrate prior to sacrificial oxide removal.
Another object of the present invention is to provide a method and apparatus of preventing oxides formed on a semiconductor substrate surface prior to gate formation.
Still another object of the present invention is to provide a method and apparatus of forming a clean surface on a semiconductor substrate to provide for a high quality gate oxide transfer.
It is also an object of the present invention to provide a method and apparatus for the uniform formation of a gate oxide layer across the surface of a semiconductor substrate.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method of eliminating metal contaminants on a surface of a semiconductor substrate. The method comprises the steps of providing a semiconductor substrate which may have metallic contaminants and/or hydrocarbon-containing contaminants on a surface thereof into a mainframe. The pressure and atmosphere of the mainframe is then evacuated to an oxygen-free environment at a pressure of less than about 1 Torr. Subsequently, the semiconductor substrate is heated to an elevated temperature, preferably to a temperature ranging from about 500xc2x0 C. to about 700xc2x0 C. for a time ranging from about 5 minutes to about 30 minutes, within the mainframe. While heating the substrate, the substrate is simultaneously purged and a surface thereof contacted with a chlorine-containing gas, preferably HCl or Cl2 by a chemical vapor deposition process, which may form volatile metallic byproducts with metallic contaminants and/or volatile byproducts with the hydrocarbon-containing contaminants thereover the substrate surface. During the heating and purging of the semiconductor substrate in the mainframe, the surface of the substrate is cleaned and/or volatile byproducts may be removed from the surface of the semiconductor substrate to provide a semiconductor substrate having a clean surface.
In the preferred embodiment, the substrate to be cleaned which may have metallic contaminants and/or hydrocarbon-containing contaminants on a surface thereof preferably comprises a silicon substrate with a plurality of block levels thereover which may contaminate the surface of the substrate by providing thereover metallic contaminants comprising metals including transition metals, inner-transition metals, and metalloids, and/or hydrocarbon-containing contaminants. Alternatively, a plurality of semiconductor substrates to be cleaned and/or which may have the contaminants on surfaces thereof may be provided into the mainframe whereby the substrates are retained by a workpiece during the heating, purging and cleaning process of removing metallic and/or hydrocarbon-containing contaminants from the surfaces of the substrates within the mainframe.
In the preferred embodiment, the apparatus for cleaning and/or eliminating metallic and/or hydrocarbon-containing contaminants on a surface of a semiconductor substrate comprises a mainframe having at least one workpiece holder adapted to hold a semiconductor substrate which may have metallic and/or hydrocarbon-containing contaminants on a surface thereof, at least one heating element adapted to heat the mainframe to an elevated temperature, at least one input line adapted to provide the chlorine-containing vapor into the mainframe, at least one output line adapted to remove the volatile byproducts from the mainframe, and at least one cooling chamber adapted to cool the semiconductor substrate having the clean surface. More preferably, the heating chamber comprises the at least one component for heating the semiconductor substrate to the elevated temperature, the at least one component for providing the chlorine-containing gas over and contacting the surface of the substrate to form the volatile byproducts with the metallic and/or hydrocarbon-containing contaminants, and the at least one component for removing the volatile byproducts from the closed heating chamber within the closed mainframe.
More preferably, the semiconductor substrate is adapted to be continuously heated in the mainframe wherein the mainframe is a closed mainframe comprising at least the heating chamber and the cooling chamber directly in contact with each other. The heating chamber of the mainframe may comprise a closed heating chamber whereby a door seals the heating chamber from at least one other chamber within the mainframe, preferably from the cooling chamber. In such an embodiment, the mainframe further comprises a means for transferring the semiconductor substrates directly from the cooling chamber to the heating chamber and vice versa. Preferably the means for transferring the semiconductor substrates from one chamber to the other is the at least one workpiece holder adapted to hold a semiconductor substrate which may have metallic and/or hydrocarbon-containing contaminants on a surface thereof comprising a pedestal whereby the substrates are provided over and secured to the pedestal.
Once the substrates to be cleaned and/or which may have metallic and/or hydrocarbon-containing contaminants on surfaces thereof are provided within the mainframe, the pressure and atmosphere of the mainframe are then evacuated to an oxygen-free environment preferably to a pressure ranging from about 50 mTorr to about 400 mTorr. In the preferred embodiment, the substrates are provided over the pedestal whereby the pedestal transfers the substrates from the cooling chamber to the heating chamber within the closed mainframe. The door then seals the heating chamber to provide the closed heating chamber whereby the semiconductor substrate is then adapted to be continuously heated in the heating chamber to the elevated temperature.
In the present invention, the chlorine-containing gas, at the elevated temperature, is adapted to clean the substrate surface and/or form the volatile metallic byproducts whereby chlorine dissociates from the chlorine-containing gas to react with the metallic contaminants thereby forming the volatile byproducts which may be removed from the surface of the substrate. Preferably, the volatile metallic and/or hydrocarbon-containing byproducts are removed from the substrate surface prior to providing a gate oxide layer over said substrate surface and prior to removal of a sacrificial oxide.